1. Field of the Invention
The present invention relates to an eyesight correcting apparatus for correcting myopia, hyperopia and astigmatism, particularly an eyesight correcting apparatus for recovering the eyesight by correcting the shape of the cornea.
2. Detailed Description of Prior Art
The eyeball has a structure consisting of, from front, the cornea followed by a crystalline lens, a vitreous body and the retina. Rays of light carrying an image passing through the cornea is converged by the crystalline lens, transmitted through the vitreous body and focused onto the retina. The image focused onto the retina is transmitted through the optic nerve connected to the retina to the brain center. The periphery of the crystalline lens is suspended with a ciliary body (ciliary zonule): the thickness of the lens is adjusted through the tension or relaxation of the ciliary body, so that the refraction of the lens may vary so as to focus the image on the retina.
Generally, the blurred vision in myopia or hyperopia can be accounted for by two mechanisms: one relates to a lowered refracting power of the crystalline lens (refractive myopia or hyperopia) which may result from the lowered functional state of the tissues such as the ciliary body responsible for adjusting the thickness of the crystalline lens as a result of exertion or aging; and the other relates to abnormal elongation of the visual axis (axial myopia or hyperopia), that is, the axis passing through the crystalline lens and retina (sclera and choroid), which may develop even when the refracting power of the lens remains normal. The axial myopia may be observed in an eyeball where the cornea and the lens are abnormally close to each other, or where the cornea is abnormally convex forward.
In any case, in myopia, when a far point is viewed, the rays from that point are brought to a focus in front of the retina, while in hyperopia, when a near point is viewed, the rays therefrom are brought to a focus behind the retina. Moreover, because the corneal surface does not represent a perfect sphere, it has more or less spherical aberrations and astigmatism, and this abnormality is compensated for generally by the crystalline lens. If this optical apparatus is disordered, astigmatism will result.
Conventionally, for the correction of myopia, hyperopia and astigmatism, spectacles and contact lenses have been employed. However, those apparatuses present with a number of disadvantages: they are cumbersome because they must be worn and removed before and after each use; and they can not be used by those who are engaged in vigorous sports or in occupations requiring only the use of unaided eyes. To compensate for those disadvantages, eyesight correcting methods have been developed and actually practiced.
The simplest method among them aims at activating the crystalline lens, and the ciliary body which is responsible for adjusting the lens: the method consists of ordering the patient to look into a cylindrical apparatus like a telescope, and to watch, in the cylinder, an object or a printed image while the object is physically moved back and forth, that is, to track the movement of the object by vision, and of resolving the impaired vision through the repetition of this exercise. However, with this method, the notable effect appears only after the patient has repeated the exercise for several tens minutes everyday for a certain period. Thus, the method requires a considerable time before it has a notable effect, that is, the method is slow in action.
Recently, the method based on laser radiation (called xe2x80x9cLASIKxe2x80x9d) is employed for the correction of myopia. This method consists of ablating the central portion of the cornea with a diameter of about 3 to 15 mm around the center of the pupil using a laser beam, so that the front-end surface of the cornea is made flat or concave. Then, the cornea serves as a concave lens, and incident rays of light carrying an image come to be appropriately refracted by the cornea, and thus the image is properly focused on the retina.
However, this method requires a high skill from the surgical operator, is highly risky, and may cause an anxiety in the patient because of the smallness of the previously treated cases, as to what change the operated cornea will undergo over several years ahead. In addition, if unfortunately the operation were unsuccessful, the operated cornea could not recover the original condition. Moreover, because the depth of ablation has a certain limitation, the method cannot be applied for correcting the high degree of myopia. As it is, for correcting the high degree of myopia, there is a known method that depends on the implantation of an intraocular lens. However, this method is not always reliable because it is not yet thoroughly clarified what complications the operation may cause, and the method is not applicable to the patients with cataract or iritis.
Recently, an eyesight correction method called xe2x80x9cortho-keratologyxe2x80x9d has attracted attention. This eyesight correction method consists of attaching a contact lens having a prescribed form to the cornea before the patient goes to bed, thereby adapting the cornea to take a specified shape during sleep. However, this eyesight correction method also has its own drawbacks: although the patient can maintain normal eyesight for a certain period after the correction contact lens is removed, the cornea resumes thereafter its original shape owing to its elasticity, that is, its eyesight correction effect is temporary, and the patient must repeat the same cornea correction procedure using the prescribed contact lens everyday, to ensure the correction effect; and further because the prescribed contact lens has a use life of several years, the patient must replace it periodically which will require a considerable cost.
As discussed above, there is no conventional correction method that is applicable to all the types of ophthalmic abnormalities. Particularly, even with the aforementioned method based on laser radiation or on ortho-keratology, it is difficult to securely correct the eye suffering from serious myopia/hyperopia, and the eye in which the cornea is depressed towards the crystalline lens.
As a result of a long-lasting study, the present inventor found that warming the cornea which is composed of keratin compounds to a specified temperature or higher softens it, and succeeded in developing a novel eyesight correction method comprising softening the cornea by warming it by any known method, modifying the shape of the softened cornea as appropriate according to the abnormal eyesight, so as to compensate for the abnormality, and quenching the thus modified cornea so that the corrected cornea may not restore its original shape owing to its elasticity.
An object of this invention is to provide such an apparatus for correcting eyesight.
Another object of this invention is to provide an eyesight correcting apparatus capable of easily correcting the deformed cornea safely without inflicting any damage to it, and of enabling the operated cornea to maintain the corrected shape over a long period or semi-permanently.
A still further object of this invention is to provide an eyesight correcting apparatus capable of, even when applied to the eye suffering from the high degree of myopia or hyperopia, or to the cornea whose front surface is depressed towards the crystalline lens, safely and securely correcting the deformed cornea in such a manner as to enable the cornea to maintain the corrected shape after the operation.
A still further object of this invention is to provide an eyesight correcting apparatus, which is so simple in structure that it is producible at a low cost, and easy for handling.
The present invention relates to an apparatus for correcting eyesight by modifying the shape of the cornea, which comprises a cornea pressure member for shaping the cornea by pressure, a warming unit of the cornea pressure member, and a cooling unit for cooling the cornea.
The present invention further comprises a micro-vibration generating unit for applying a micro-vibration to the cornea pressure member.
The present invention further comprises a cornea sucking member for modifying the shape of the cornea by sucking, in addition to or instead of the cornea pressure member.
When the eyesight correcting apparatus of this invention is used, it is necessary to soften the cornea in advance by warming the eyeball by any known method.
The cornea pressure member is for modifying the shape of the softened cornea to any desired shape such as a convex or concave spherical shape, flat shape, etc., according to the given condition to be corrected. Its material may be chosen from any synthetic resins, metals, non-metal elements, etc., as long as it is safe and sanitary even when it is brought into contact with the cornea. The cornea pressure member may apply a pressure on the cornea in the form of a hydrostatic pressure or an air pressure.
The warming unit of the cornea pressure member is for maintaining the softened state of the cornea produced at a preparatory stage, and for preventing the temperature of the cornea from being lowered through the contact with the pressure-based cornea shaping unit. The warming unit may be based on nickel-chromium wire heating, module alloy heating, laser heating, microwave heating, warm water reflux heating, etc. If the cornea pressure member is based on hydrostatic or air pressure, it is possible to utilize pressurized water or air heated to a predetermined temperature.
The cornea cooling unit is for rapidly cooling (quenching) the operated cornea kept at a warm state, thereby stabilizing the corrected shape of the cornea. The unit may take any desired shape and structure as long as the above object is satisfied, and is permanently or detachably attached to the cornea pressure member, independently of the cornea sucking member. The cooling mode may include water- or air-cooling. One preferred example of the cornea cooling unit operates by ejecting a cooling liquid kept in a syringe or pipette towards the cornea from the injection port of the cornea sucking member.
The cornea warmed to a predetermined temperature or higher is softened: tissue cells become relaxed and expanded. Therefore, it is possible to correct the shape of the cornea with the aforementioned cornea shaping member and then to stabilize the corrected shape by rapidly cooling the cornea via a cooling liquid, because then the tissue cells of the cornea contract in a moment to stabilize the corrected shape. This quenching procedure resembles quite well the quenching of a metal, which comprises rapidly cooling a metal modified in texture by previous heating to stabilize the modified metal texture so firmly that the metal will never resume the original texture over time. Similarly, this procedure prevents the operated cornea from resuming the original shape.
The micro-vibration generating unit may be used a small vibrator adjustable in the rate and intensity of vibrations, and is for applying a micro-vibration to the cornea via the cornea pressure member. This unit facilitates the tissue cells of the cornea, which have been subjected to warming to be further, softened and activated. It is also possible to modify the shape of the cornea bit by bit through the pressure worked via the micro-vibration.
The cornea sucking member takes, for example, a semi-spherical, cap-like form, and when it is attached to the cornea, a defined space is formed between the inner surface of the cap and the front surface of the cornea. The radius (R) of the cap can be varied to any desired value to match the given corrected shape of the cornea.
The vacuum sucking unit may incorporate any sucking machine such as a small vacuum pump, suction syringe, vacuum vessel containing a cartridge with an evacuated internal space, etc., as long as it has a sucking power sufficiently strong to cause the softened cornea to bulge forward. The cornea sucking unit may be provided with the aforementioned warming unit.
According to the present invention, the cornea pressure member may be combined with the cornea sucking member such that it can be slid over the latter.
According to one embodiment of this invention, the cornea sucking member takes a cap-like shape, and it causes a negative pressure to develop in the space between the member and the front surface of the cornea, in such a manner as to cause the cornea to be modified in its shape. The cornea pressure member comprises a rod portion which penetrates the cornea sucking member to slide therethrough, and a head portion attached to the distal tip end of the rod portion. A cooling liquid injection channel is formed through both the rod and head portions.
The cornea sucking member has a medicine injection port through which it is possible to dispense a liquid medicine to the cornea as needed, so that the surface of the cornea can be kept moist, and thus the cornea be prevented from drying and hardening which would otherwise result during the cornea being subject to the correction procedure.